Intact seeds of common milkweed (Asclepias syriaca L.) were innately dormant at maturity in October. Stratification was effective in overcoming dormancy, and nondormant seeds germinated in both light and darkness. One week of stratification was effective in overcoming dormancy in some of the seeds; seeds stratified in light and then incubated in darkness at 30/15 C germinated to 75.3%. Seeds stratified in light or darkness for 2 and 3 weeks and then incubated in light or darkness germinated to 68% or more at thermoperiods of 35/20 and 30/15 C but germinated to 20% or less at 20/10 C. Seeds stratified for 9 weeks also germinated to high percentages (70% or more) at 20/10 C. Seeds planted in a nonheated greenhouse in October germinated the following spring and most of the germinatoin occurred between 4 April and 5 May, when the mean maximum and minimum daily temperatures were 20.5 and 9.1 C, respectively.